The Navy SEAL Physical Fitness Guide - Human Performance

160 Plyometrics

Plyometric training is very intense, highly specific,

and if done improperly it may be injurious. It should

not be routinely incorporated in the Naval Special

Warfare physical training programs.

How Plyometrics Work

Plyometric exercises help to develop explosive strength and speed in fast twitch

muscle fibers. These exercises use the inherent stretch-recoil properties of muscle (i.e.,

eccentric tension generated when the muscles are lengthened) to enhance subsequent

shortening or concentric contractions. This is the dynamic action behind the rapid pre-

stretch or “cocking” phase to “activate” these natural recoil properties. Examples of this

phase include taking the arm back into position prior to throwing a baseball or bending the

knees prior to jumping. Thus athletes that rely on explosive strength and speed, such as

sprinters and basketball players, include plyometrics in their training programs. A

plyometric movement can be broken down into three phases:

" Lengthening phase (eccentric contraction).

" Amortization phase.

" Take-off (concentric contraction).

Figure 9-1. Three

Phases of

Plyometrics:

Lengthening,

Amortization and

Take-Off

During the lengthening

phase, the muscle creates

tension like a spring being

stretched. This type of

contraction, called an eccentric

contraction, occurs when

performing movements such as jumping down from an object, running downhill, or

lowering a weight. During an eccentric contraction, tension is built into the muscle as it

LENGTHENING

AMORTIZATION

TAKE-OFF